In Hugin, straight line control points are used within a single image, not as a shared feature across multiple images. To add one, show the same image on both sides and mark the two endpoints of the straight feature in that image.

So if the same edge appears in three photos, add a straight line separately for each photo where it appears. The line name generally does not matter for linking images together.

For alignment between photos, still add normal matching control points between the images, ideally along that same feature. In practice, the best results come from:

• defining the straight line accurately in each individual photo
• adding matching control points between overlapping photos along the line

This helps Hugin model distortion in each image while also aligning the images to each other.